USPTO Patents Application 10777120

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G100014541

METHOD OF PRODUCING LEAD ZIRCONATE TITANATE-BASED
THIN FILM, DIELECTRIC DEVICE AND DIELECTRIC THIN FIL

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method of
producing a lead zirconate titanate-based thin film
having excellent dielectric characteristics, a
dielectric device including the same and a dielectric
thin film.

Related Background Art

Of ferroelectric materials, lead-based
ferroelectric materials such as PZT and PLZT are most
practically used, because of their large residual
dielectric polarization. Ferroelectric materials
having been practically used, such as PZT and PLZT,
are materials of sintered bulk, that is, multi-
crystals whose orientations have not been controlled.
In sintered bulk PZT, its characteristics such as
permittivity and electric-mechanical bond coefficient
are known to reach a maximum at morphotoropic phase
boundary (MPB) in the vicinity of Zr/(Zr + Ti) = 0.52

Ferroelectric thin films of, for example, PZT
and PLZT have a good chance of being used in many
applications, such as ferroelectric memory and
actuator. As to the ferroelectric thin films which
are considered most promising in terms of the

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10

technique for controlling crystal orientation,
crystal orientations of (100)/ (001) have been used
because of ease of film-forming and film-synthesizing,
and there have been performed almost no film.-
syntheses nor film-characteristic evaluation adopting
other crystal orientations; accordingly, it has not
been -clarified that ^excellent characteristics are
shown by which orientation.

There have been examined ferroelectric thin
films, such as PZT and PLZT, which have been formed
by sputtering and sol-gel processing (Japanese Patent
Application Laid-Open No. 2003-17767, Japanese Patent
Application Laid-Open No. 6-350154); however, the
inventors of this invention have been examining the
formation of ferroelectric films, such as PZT and
PLZT, by metal organic chemical vapor deposition
(MOCVD) (Japanese Patent Application Laid-Open No.
2001-220676) .

In sintered bulk PZT, as to its optimal
composition, the characteristics such as permittivity
and electric-mechanical bond coefficient are known to
reach a maximum at morphotoropic phase boundary (MPB)
in the vicinity of Zr/(Zr + Ti) = 0.52; however,
there have also been reported different values of the
25 optimal composition of morphotoropic phase boundary,
for example, Zr/(Zr -h Ti) = 0.80, and moreover, the
composition has not been shown yet which have the

20

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most excellent characteristics.

Accordingly, in PZT thin films, it is not
clarified yet with what orientation and composition
they show the most excellent characteristics.
5 Ferromagnetic thin films of, for example, PZT

having been reported up until now are mostly one-axis
orientation films, but not epitaxial crystal thin
films .

10 SUMMARY OF THE INVENTION

In the light of the actual state of the prior
arts, the inventors of this invention have searched
for a combination of crystal orientation and
composition which is not known, but may provide

15 ferroelectric thin films with excellent

characteristics, while producing excellent epitaxial
crystal thin films of PZT and PLZT and evaluating the
orientation and composition dependency thereof.
Accordingly, the object of this invention is to

20 provide epitaxial crystal thin films formed based on
PZT and PZLT both having a special combination of
crystal orientation and composition that provides
excellent characteristics to the thin films, the
application of such thin films, and a method of

25 producing the same.

To accomplish the above object, the inventors
have successfully produced excellent epitaxial

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10

crystal thin films of PZT and PLZT by MOCVD. And
they have found, after the evaluation of the
orientation and composition dependency of the thin
films, that there exists a special combination of
crystal orientation and composition that gives
feroelectric thin films excellent characteristics
beyond expectation. Consequently, the present
invention provides:

(1) a lead zirconate t itanate-based thin film,
characterized in that it is an epitaxial crystal th.i.n
film which has a chemical composition represented bv
the general formula Pbi-, Ln x ZryTii.^Os (wherein I,n
represents any one selected from the group consisting
of lanthanoid elements including lanthanum, niobium,
15 calcium, barium, strontium, iron, manganese and tin;
and 0<x<l, 0.43<y<0.65) and whose orientation is
{111} (including orientations whose tilt angle from
the direction perpendicular to the substrate surface
is within IS") ;

^° (2) the lead zirconate titanate-based thin film

according to the above description (1), wherein the
orientation of the film is (111) (including
orientations whose tilt angle from the direction
perpendicular to the substrate surface is within

25 15") ;

(3) the lead zirconate titanate-based thin film
according to the above description (1), wherein the

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10

half-width of the locking curve in the
circumferential direction of X-ray pole figure is
within 30";

(4) the lead zirconate t itanate-based thin film
according to the above description (1), wherein the
half-width of the locking curve in the
circumferential direction of X-ray pole figure is
within 15°;

(5) the lead zirconate titanate-based thin film
according to the above description (1), wherein the
half-width of the locking curve of the crystal is
within 15°;

(6) the lead zirconate titanate-based thin film
according to the above description (1), wherein the

15 half-width of the locking curve of the crystal is
within 5°;

(7) the lead zirconate titanate-based thin f.i Im
according to the above description (1), wherein the
half-width of the locking curve of the crystal is

20 within 2°;

(8) the lead zirconate titanate-based thin film
according to the above description (1), wherein the
half-width of the locking curve of the crystal is
within 1°;

(9) a lead zirconate titanate-based thin film
having a composition represented by the general
formula Pbi-xLnxZryTia.yOj (wherein Ln represents any

25

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10

15

20

25

one selected from the group consisting of lanthanum,
lanthanoid elements, niobium, calcium, barium,
strontium, iron, manganese and tin; 0<x<l; and
0.43<y^0.57) , characterized in that its relative
permittivity - voltage characteristics satisfy the
following equation: Ag/AE^3.0, wherein Ag is a change
in relative permittivity and AE is a change in
electric field strength (kv/cm) ;

(10) the lead zirconate titanate-based thin
film according to the above description (9), wherein
its relative permittivity - voltage characteristics
satisfy the following equation: Ae/AE>5.0;

(11) the lead zirconate titanate-based thin
film according to the above description (9), wherein
the film is an epitaxial film whose orientation is
(111) or within 15° from (111);

(12) the lead zirconate titanate-based thin
film according to the above description (1) or (11),
wherein the {111} face of the epitaxial film is
orientated within a tilt angle of 5° (including 0°);

(13) the lead zirconate titanate-based thin
film according to the above description (1) or (12),
wherein the {111} face of the epitaxial film is
orientated within a tilt angle of 3° (including 0°);

(14) the lead zirconate titanate-based thin
film according to the above description (1) or (9),
wherein silicon is used for the substrate;

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10

(15) the lead zirconate t itana te-based thin
film according to the above description (14), wherein
the silicon is (100) orientated;

(16) the lead zirconate ti tanate-based thin
film according to the above description (14), wherein
the silicon is (111) orientated;

' (17) the lead zirconate ti tanate-based thin
film according to the above description (1) or (9),
wherein the film is formed by MOCVD;

(18) the lead zirconate ti tana te-based thin
film according to the above description (1), wherein
in the general formula Pbi-^ Ln ^ 2ryTix_y03,
0 . 4 3<y<0 .57;

(19) the lead zirconate titanate-based thin
film according to the above description (18), wherein
in the general formula Pbi-.^ Ln x ZryTii.yO.,
0.4 5<y<0.55;

(20) the lead zirconate titanate-based thin
film according to the above description (1) or (9),
wherein the crystal structure is at least any one of
tetragonal, cubic and rhombohedral crystals;

(21) the lead zirconate ti tana te-based thin
film according to the above description (20), wherein
at least any two of tetragonal, cubic and

25 rhombohedral crystals coexist;

(22) the lead zirconate ti tanate-based thin
film according to the above description (1) or (9),

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20

wherein at least the surface of the substrate is
electrically conductive ;

(23) a lead zirconate t i tanate-based thin film,
characterized in that it is an epitaxial crystal thin
film which has a chemical composition represented by
the general formula Pbi-x Ln x Zri-yTiyOs (wherein Ln
represents any one selected from the group consisting
of lanthanum, lanthanoid elements, niobium, calcium,
barium, strontium, iron, manganese and tin; and 0<x<l
0,40<y<0.65) , whose orientation is {111} (including
orientations whose tilt angle from the direction
perpendicular to the substrate surface is within 15°)
and in which at least any two of tetragonal, cubic
and rhombohedral crystals coexist;

(24) the lead zirconate ti tanate-based thin
film according to the above description (23) , wherein
in the general formula Pbi.^ Ln « Zri-yTiyOs,

0 . 4 3<y<0 . 57;

(25) a lead zirconate titanate-based epitaxial
thin film formed by MOCVD, characterized in that it
has a chemical composition represented by the general
formula Pbi-x Ln , Zra-yTiyOs (wherein Ln represents any
one selected from the group consisting of lanthanum,
lanthanoid elements, niobium, calcium, barium,
strontium, iron, manganese and tin; and 0<x<l,
0.43<y<0.65) and its orientation is {111} (including
orientations whose tilt angle from the direction

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perpendicular to the substrate surface is within
15°) ;

(26) a dielectric device, including the lead
zirconate t i tanate-based thin film according to any
5 one of the above descriptions (1), (9), (23) and
(25) ;

' (27) a piezoelectric device, including the lead
zirconate titanate-based thin film according to any
one of the above descriptions (1), (9), (23) and
10 (25);

(28) an ink jet printer head, including the
piezoelectric device according to the above
description (27);

(29) a ferroelectric device, including the lead
zirconate titanate-based thin film according to any
one of the above descriptions (1), (9), (23) and
(25) ;

(30) a pyroelectric device, including the lead
zirconate titanate-based thin film according to any
one of the above descriptions (1), (9), (23) and
(25) ;

(31) a method of producing a lead zirconate
titanate-based thin film, characterized in that a
crystal film having a chemical composition

25 represented by the general formula Pbi-xLnx2ri.yTiy03
(wherein Ln represents any one selected from the
group consisting of lanthanum, lanthanoid elements.

15

20

niobium, calcium, barium, strontium, iron, manganese
and tin; and 0<x<l, 0.43<y<0.65) is epitaxially grown
on a substrate at least the surface of which has a
{111} orientation or orientation with a tilt angle
within 15"^ from {111} by MOCVD;

(32) the method of producing a lead zirconate
titanate-based thin film according to the above
description (31), wherein 0.43<y<0.57;

(33) . the method of producing a lead zirconare
titanate-based thin film according to the above
description (31), wherein 0.45<y<0.55; and

(34) a lead zirconate titanate-based thin film,
characterized in that it is a crystal thin film which
has a chemical composition represented by the general
formula Pbi-x Ln ^ Zri.yTiyOa (wherein Ln represents any
one selected from the group consisting of lanthanum,
lanthanoid elements, niobium, calcium, barium,
strontium, iron, manganese and tin; and 0<x<l,

0 . 40^y<0 . 65) , whose orientation is {111} (including
orientations whose tilt angle from the direction
perpendicular to the substrate surface is within 15^)
and in which at least any two of tetragonal, cubic
and rhombohedral crystals coexist.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG, 1 is a schematic view showing an epitaxial
crystal, a one-axis crystal and a multi-crystal and a

schematic view of pole figure patterns of X-ray
diffraction;

FIGS. 2A, 2B, 2Cr 2D and 2E are schematic views
showing the coexisting state of different crystal
structures in the epitaxial films of this invention
under no influence of an electric field;

- FIG. 3 is a schematic view of one example of
MOCVD apparatuses;

FIG. 4 is an illustration of the vertical MOCVD
apparatus used in the examples of this invention;

FIG. 5 is an illustration of the nozzle of the
MOCVD apparatus used in the examples of this
invention ;

FIG, 6 is a view showing the XRD patterns of
the PZT films formed on a ( 1 1 1 ) SrRuOj// ( 1 1 1 ) SrTi03
substrate and having composition ratios of y = 0.7 5
(rhombohedral crystal), y = 0.48 (morphotoropic phase
boundary) and y = 0.39 (tetragonal crystal),
respectively;

FIG. 7 is a view showing an X-ray reciprocal
mapping image of the (222) face of PZT;

FIG. 8 illustrates the composition dependency
of the lattice constant of PZT;

FIG. 9 illustrates the composition and crystal
orientation dependency of the relative permittivity
Br of PZT films;

FIG. 10 illustrates the composition and crystal

orientation dependency of the polarization-voltage
characteristics (P-E characteristics) of PZT films;

FIG, 11 illustrates the composition and crystal
orientation dependency of the relative permittivity-
voltage characteristics (C-E characteristics) of PZT
films ;

- FIG. 12 illustrates the composition and crystal
orientation dependency of the piezorestricti vi ty-
voltage characteristics (S-E characteristics) of PZT
films;

FIG. 13 illustrates S-E curves of (100)
orientated^ (110) orientated and (111) orientated PZT
films having a composition ratio y = 0.48
(morphotoropic phase boundary) when applying unipolar
electric field;

FIG- 14 summarizes and schematically
illustrates the composition and crystal orientation
dependency of the relative permittivity 8r,
spontaneous polarization Ps, coercive electric field
Ec and residual dielectric polarization Pr of PZT
films;

FIG. 15 is a view showing an X-ray reciprocal
mapping image of the (114) face of a (111) orientated
PZT epitaxial film having a composition ratio of
2r/ (Zr + Ti) = 0.53;

FIG. 16 is a graph showing the relationship
between the value of piezorest rict ivi ty and Zr/(Zr +

Ti) ratio of the PLZT film formed in the example of
this invention;

FIG. 17 is a view showing the X-ray diffraction
charts of the PLZT films formed on a
(lll)Pt//(100) YSZ//(100)Si substrate and a
(lll)Pt//(lll) YSZ//(lll)Si substrate; and

- FIG. 18 is a view showing the X-ray diffraction
chart of the PLZT film formed on a
(111 ) Pt// (100) YSZ// (100) Si substrate ,

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention has been made based on the
inventors' finding that a lead zirconate titanate-
based epitaxial thin film having the most excellent
dielectric characteristics is obtained by forming a
lead zirconate t itanate-based thin film represented
by the general formula Pbi-,xLnxZri..yTiy03 (wherein Ln
represents any one selected from the group consisting
of lanthanum, lanthanoid elements, niobium, calcium,
barium, strontium, iron, manganese and tin; and
0<yi<l) so that it has a specific composition
(0. 43<y<0. 65) and a specific crystal orientation
[{111) orientation or any one of orientations whose
tilt angle from the direction perpendicular to the
substrate surface is within 15°] .

Typical examples of lead zirconate titanate-
based dielectrics, such as PZT and PLZT, which are

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represented by the general formula Pbi^^Ln^Z r i.^TiyOa
(wherein Ln represents any one selected from the
group consisting of lanthanum, lanthanoid elements,
niobium, calcium, barium, strontium, iron, manganese
5 and tin; and 0^x<l, 0<y<l) are: Pb(Zr, Ti)03 [PZT] and
(Pb, La) {Zr, Ti)03 [PLZT]. PZT and PL2T are
preferable lead zirconate ti tanate-based dielectrics.
And it is known that if part of Pb of the PZT is
replaced with La, the performance of the dielectric
10 is improved and that if the same is replaced with Nb
etc., the sim.ilar performance is also obtained. When
part of Pb is replaced with La, the amount of La used
for the replacement is preferably 0<x<0.15, more
preferably 0.04<x<0.12. The same is true for the
15 other elements.

The inventors successfully made possible the
epitaxial growth of lead zirconate t itana te-based
crystals especially by MOCVD, and a closer
investigation was made while changing the composition
20 and orientation of the lead zirconate ti tanate-based
crystals .

Whether the formed film is an epitaxial crystal
(single crystal ; complete orientation) or a one-axis
orientation crystal or a mul t i~crystal (random
25 orientation) can be distinguished by the pattern of

the pole figure of X-ray diffraction, as shown in FIG.
1. An epitaxial crystal is a crystal in which

crystal grains are oriented completely in the same
direction in all the crystalline regions, and spots
of n-time symmetry appear in the pole figure as shovj
in the left of FIG. 1 (FIG. 1 shows that spots of 4-
time symmetry appear when observing the 110 face of
an epitaxial crystal having 100 orientation and for
an epitaxial crystal having 111 orientation, FIG. 6
shows that spots of 3~time symmetry appear). In th.i 5
case, the half-width of the spots in the
circumferential direction is preferably within 30"=^,
more preferably within 15^ and particularly
preferably within 10°. A one-axis orientation crysta
is a crystal in which crystal grains are oriented in
the same direction relative to one axis in each
crystalline region, but are rotated mutually in a
plane- A ring-shaped diffraction pattern appears in
the pole figure as shown in the middle of FIG. 1. A
multi-crystal is a crystal in which crystal grains
are orientated at random in each crystal region, and
a diffraction pattern of the whole circle appears in
the pole figure, as shown in the right of FIG. 1.

A method of forming a lead zirconate tltanate-
based film itself, which uses MOCVD, is disclosed in
Japanese Patent Application Laid-Open No. 2001-22067^
(Japanese Patent Application No. 2000-32817) by the
inventors of this invention, and it will be briefly
described later.

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15

20

25

The lead zirconate ti tana te-based thin film oi
this invention is a lead zirconate t itanate-based
thin film of PZT and PLZT represented by the general
formula Pbi^^Ln^Zr i-yTiyOa (wherein Ln represents any
one selected from the group consisting of lanthanum,
lanthanoid elements, niobium, calcium, barium,
strontium, iron, manganese and tin; and 0<x<l),
characterized in that it has a composition in which v
falls in the rage of 0.43<y<0.65, preferably in the
rage of 0.43<y<0.60, more preferably in the rage of
0.43<y<0.57 and much more preferably in the rage of
0,45<y<0.55 and it is an epitaxial film having a
{111} orientation or any one of orientations whose
tilt angle from the direction perpendicular to the
substrate surface is within 15°.

Closer examination by the inventors have shown
that selectively outstanding dielectric
characteristics (P-E characteristic, P-S
characteristic), which are different from those of an
extension of the characteristics of the films of
tetragonal crystal alone or rhombohedral crystal
alone, are observed in the lead zirconate titanate-
based thin film having a composition siach that y =
around 0.52, which may be a morphotoropic phase
boundary, in particular y falls in the range of
0.45<y^0.65 and having an orientation {111}. The
composition is preferably such that y is in the range

of 0.43<y<0.60, more preferably in the rage of
0.43<y<0.57, and particularly preferably in the rage
of 0.4 5<y<0.55. With y beyond 0.65, the effect of
improving the dielectric characteristics is small.
With y equal to or more than 0.40, the effect of
improving the elect rostriction characteristics is
detected; however, with y less than 0.43, undesirably
the characteristics such as residual dielectric
polarization value Pr and relative permittivity r.
tend to deteriorate.

Further, examination by the inventors has also
showed that there exists a film of the PZT having a
composition in the above described range where at
least any two of tetragonal, cubic and rhombohedral
crystals coexist. It has not been known up until now
that there coexists any two or three of tetragonal,
cubic and rhombohedral crystals in the PZT system.
In this invention tetragonal crystal and cubic and/or
rhombohedral crystal may coexist, and besides, cubic
and rhombohedral crystals may also coexist.

The coexisting state of these different crystal
structures may be as shown in FIGS. 2A to 2E under no
influence of an electric field. FIG. 2A shows a two-
layer structure in which two or more different
crystals (tetragonal, cubic and rhombohedral
crystals) are stacked in the film thickness direction.
FIG. 2B shows a multilayer structure in which two or

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10

more different crystals are stacked into multiple
layers. In the above figures, the thickness if each
layer is shown uniformly; however, the thickness may
be nonuniform and a portion of discontinuity may
exist in part of the layers. FIG. 2C shows a state
in which two or more different crystals coexist side
by side in the direction other than that parallel to
the substrate surface. FIG. 2D shows a state in
which the regions of two or more crystals are
dispersed and intermingled not in a maldistributed
manner, but in an almost uniform manner. FIG. 2E
shows a state in which the regions of two or more
crystals are dispersed and intermingled not in a
maldistributed manner in the film thickness direction,
15 but in a maldistributed manner in the film surface

direction. It is to be understood that the films in
accordance with this invention act as a mixed crystal
of two or more crystal phases as a whole and exert
ferroelectric characteristics which are different
from an extension of the characteristics of each
crystal phase, and therefore, the structures of FIGS.
2A to 2C are different from macroscopic stacking
structures having the characteristics of the
respective crystal phases as they are (the simply
totalized characteristics) or from structures in
which macroscopic regions are intermingled. Of the
structures shown in FIGS. 2A to 2E, those of FIGS. 2C

20

25

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10

15

20

25

to 2E are preferable.

The films of this invention have a {111}
orientation. Most preferably they have a (111)
orientation. In the following this invention will
sometimes be described in terms of the films having a
(111) orientation; however, it is to be understood
that -such description also applies for the other
films having a {111} orientation. Further, the films
having orientations whose tilt angle from the
direction perpendicular to the substrate surface is
within 15° are also included in the films of this
invention, because they can have the same
characteristics as the films having a {111}
orientation. In the films of this invention, though
the tilt angle is within 15°, the smaller tile angle,
the better. Therefore, the tilt angle is preferably
5° or less, more preferably 3° or less, and the films
having a complete {111} orientation are the most
preferable. Preferably the crystals having a {111}
orientation and orientations whose tilt angle is
within 15° account for at least 70% of the total
amount of crystals, preferably 80% or more, much more
preferably 90% or more, and particularly preferably
100% .

The completeness of the crystal orientation of
a film can be evaluated by the half-value width of a
locking curve. Preferably the half-value width of a

locking curve is 15° or less, more preferably 5° or
less, much more preferably 2"* or less, and
particularly preferably 1^ or less. That the
completeness of epitaxial orientation of a film can
be evaluated by the half-value width in the film's )
ray pole figure has been already described above.
For example, the half-value width at 20 = 38.3^ for
PZT is preferably 15° or less, more preferably 5° or
less, still more preferably 2° or less, and most
preferably 1° or less.

The second aspect of this invention is a lead
zirconate t itanate-based thin film having a
composition represented by the general formula ?bi-
xLnxZryTii^yOs (wherein Ln represents any one selected
from the group consisting of lanthanum, lanthanoid
elements, niobium, calcium, barium, strontium, iron,
manganese and tin; 0<x<l ; and 0 . 4 3<y^0 . 55 ) ,
characterized in that its relative permittivity -
voltage characteristics (C-E characteristics) satisf
the following equation: As/AE>3.0, wherein As is a
change in relative permittivity and AE is a change i
electric field strength (kv/cm). In the^ above lead
zirconate ti tanate-based thin film, preferably
As/AE>5, and more preferably the film is an epitaxia:
film having a crystal structure of a (111)
orientation or any one of orientations whose tilt
angle from the direction perpendicular to the

substrate surface is within 15°.

The C-E characteristics are characteristics
shown in FIG. 11. The relative permittivity changes
with the electric field strength as shown in the same
figure. As is the difference between the maximum and
the minimum of the relative permittivity and AE is
the difference in electric field strength which
creates the difference between the maximum and the
minimum of the relative permittivity. The Ae/AE is
calculated using the following equation: As =b1 - s2,
wherein si is the maximum relative permittivity
measured in the coercive electric field Ec (kv/cm)
and s2 is the minimum relative permittivity measured
at a electric field strength of -2Ec. AE is the
difference between the coercive electric field Ec,
which allows the relative permittivity to be the
maximum, and -2Ec, and therefore, the absolute value
of AE is 3Ec.

When the C-E characteristics have a good
symmetry as shown in FIG. 11, any one of the maximum
relative permittivity values in the positive electric
field and in the negative electric field can be
selected for the value si. However, when the C-E
characteristics do not have a symmetry and the
maximum relative permittivity values are different in
the positive electric field and in the negative
electric field, the larger value is employed. For

the films having C-E characteristics v/hose curves cic
not have an intersection in an electric field of 0,
the A8/AE is calculated by determining the value AE
while letting the electric field strength at which
the curves have an intersection be 0 . In the
conventionally used PZT thin films, such as (100)
film- having the above composition where y = 0.48, th
change in relative permittivity is small and the
value Ae/AE is 2.5 at best. The inventors of this
invention have found that a lead zirconate titanate-
based thin film develops especially good
piezoelectric characteristics when the value
A8/AE>3.0 or more.

The third aspect of this invention is a lead
zirconate ti tana te-based thin film having a
composition represented by the general formula Pbi..
xLnxZri-yTiyOs (wherein Ln represents any one selected
from the group consisting of lanthanum, lanthanoid
elements, niobium^ calcium, barium, strontium, iron,
manganese and tin; 0<x<l ; and 0 . 40<y<0 . 65 ) ,
characterized in that it is an epitaxial film which
has a {111} orientation or any one of orientations
whose tilt angle from the direction perpendicular to
the substrate surface is within 15^ and in which
tetragonal, cubic and rhombohedral crystals coexist.
In this invention, the inventors have found a crystal
film which has a {111} orientation and in which

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10

tetragonal, cubic and rhombohedral crystals coexist
in the vicinity of the morphotoropic phase boundary.
The high dielectric characteristics of the film
described in connection with the first aspect of this
invention may be attributed to the coexistence of at
least two of tetragonal, cubic and rhombohedral
crystals .

The fourth aspect of this invention is a lead
zirconate titanate-based thin film formed by MOCVD,
characterized in that it is an epitaxial film which
has a composition represented by the general formula
Pbi-xLnxZri-yTiyOs (wherein Ln represents any one
selected from the group consisting of lanthanum,
lanthanoid elements, niobium, calcium, barium,
strontium, iron, manganese and tin; 0^x<l; and
0.40Sy<0.65) and has a {111} orientation or any one
of orientations whose tilt angle from the direction
perpendicular to the substrate surface is within 15°.
The use of MOCVD enables the formation of an
excellent epitaxial film.

The method of producing a lead zirconate
titanate-based thin film which uses MOCVD will be
described below. In this invention, preferably a
lead zirconate titanate-based thin film is formed by
25 MOCVD; however, other methods such as sputtering and
sol-gel process can also be employed as long as they
allow the formation of a lead zirconate titanate-

15

20

based thin film as specified in the first to third
aspects of this invention.

In MOCVD, starting materials for forming a film
of a lead zirconate titanate-based material as
described above are not limited to any specific ones,
and starting materials well known as those used for
forming a lead zirconate titanate-based material by
MOCVD can be used as they are. In other words, they
can be vaporizable organometallic compounds that
contain metals for forming a lead zirconate titanate-
based material. In general, alkyl metallic compounds
alkoxy metallic compounds, alkyl alkoxy metallic
compounds, p-diketone compounds, cyclopentadienyl
compounds and halogenides are used-

In PZT, if { (CH3) 3CCO)2CH- is represented by thd,
examples of Pb materials include: PbCCzHs)^, Pb(thd)2,
(C2H5)3PbOCH2C(CH3)3, Pb(C2H5)3 (t-OC^Hs), Pb(CxiHi90^),,
Pb(CH3)4, PbCl4, Pb(n-C3H7)4, Pb(i-C3H7)4, PbCCgHs). and
PbCl2, examples of Zr materials include: Zr ( t-OC4H9) 4 ,
Zr(i-C3H7)4, Zr(thd)4, Zr CI,, Zr (C5H5) 2CI2, Zr(OCH3)4,
Zr(OC2Hs)4, Zr (n-OCsHii), and Zr(C2H602)4, and examples
of Ti materials include: Ti { i-OCaH, ) 4 , Ti(thd)2(i-
OC3H,)2, Ti(OC2H5)4, Ti CI4, Ti(OCH3)4, Ti(OCH9)4and
Ti(OC5Hii)4. In PZT, part of its Pb is sometimes
replaced with La; in such a case. La (thd) 3, La
{C2H602) 4 and LaCl3 can be used as La materials. Many
of these materials have the problems of not only

being toxic, but being in the solid or liquid state
at room temperature and .having low vapor pressure,
therefore, their vapor pressure need to be increased
by heating.

In the method of this invention, MOCVD can be
carried out under the same conditions (reactor,
materials, material composition, substrate, substrate
temperature, etc.) as those commonly employed in
MOCVD. Material gases can be supplied intermittently
In the following the method of forming a film of this
invention will be described in more detail, though
the description is not intended to limit this
invention .

To introduce a mixed gas, as a material,
uniformly into a reactor, it is preferable to mix
material gases prior to the introduction into the
reactor. To prevent oxidation reaction, which
inhibits the formation of the single crystal film,
from progressing in piping, it is preferable to
control the temperature of the piping. In PZT system,
the heating temperature is preferably SO'^C to 250°C,
more preferably 35°C to 200^C, and much more
preferably 35°C to 150^C, though it depends on the
type of materials. If the temperature is too high,
decomposed matter of oxides, carbides or the like is
deposited in the piping, which might make the stable
film formation difficult.

The substrate temperature is preferably 450^C t
800^C, more preferably SOO^C to 750°C, and much more
preferably 550^C to 720^C. Although the film
formation can be carried out without rotating the
substrate, if it is carried out while rotating the
substrate, the rotational speed is preferably 0.01
rpm to 100 rpm, more preferably 0.1 rpm to 50 rpm,
and much more preferably 0.1 rpm to 15 rpm.

As a carrier gas, an inert gas is selected, and
preferable carrier gases include, for example, Ar, N
and He. The mixed system thereof can also be used as
a carrier gas. The flow rate of these carrier gases
is preferably 10 cm^/min to 1000 cmVmin, more
preferably 20 cmVmin to . 750 cmVmin, and much more
preferably 50 cm^/min to 500 cmVmin.

The bubbling time of liquid materials before
the formation of a film is preferably 5 min to 2 hrs
and more preferably 10 min to 1 hrs, . though it
depends on the structure of the apparatus used.
Starting the film formation without setting such
bubbling time might result in inferior composition
control of the film formed at the beginning.

As a purge gas, the same type of gas as the
carrier gas is selected. The flow rate of the purge
gas is preferably 10 cmVmin to 20000 cm^/min, more
preferably 50 cm^/min to 10000 cmVmin, though it
depends on the purge time. If the flow rate is too

- 2.1 -

low, the film formation might take too long a time,
resulting in decrease in film forming rate, whereas
if the flow rate is too high, the substrate
temperature might decrease , causing adverse effect
5 on the film quality.

As an oxidizing gas, oxygen gas or oxygen-
nitrogen mixed g as is used. The flow rate of the
oxidizing gas is preferably 10 cmVmin to 5000 crnvmin,
more preferably 20 cmVmin to 2000 cmVmin, and much
10 more preferably 30 cmVniin to 1000 cmVmin. Because
of the flow rate control of each of the above
described gases, the total pressure of the reactor is
preferably 0.05 torr to 100 torr, more preferably 0.1
torr to 30 torr, and much more preferably 0.5 torr to
15 10 torr. The partial pressure of oxygen is

preferably 0.04 torr to 80 torr, more preferably 0.1
torr to 25 torr, and much more preferably 0.5 torr to
10 torr.

A nozzle can be used to feed material gases
onto the substrate surface, and the shape of the
nozzle used is preferably such that its opening is
narrowed toward the substrate. To make the film's
inside uniform, the opening of the nozzle is
preferably circular. The distance between the nozzle
and the substrate is preferably 0.5 nun to 40 mm, more
preferably 1 mm to 20 mm, and much more preferably 2
mm to 10 mm. The distance outside the above range

20

25

f

- 28 -

might result in inferior film surface roughness.

With such a nozzle, the film forming rate fall,
in the preferable range of, not limited to, about 0.
^m/hr to 5 fxm/hr, thereby a single crystal film is
obtained in a stable manner.

PZT as a preferable lead zirconate titanate-
based material for this invention is as follows.

PZT is represented by the general formula Pb(Zr
TiO)3; however, PZT in which part of Pb has been
replaced with La, that is, (PLZT) or with Nb or Ca i
referred to broadly as PZT system. PbTiOj and PbZrOs
form a complete solid solution and become a
ferroelectric material in the wide Zr/Ti ratio range
except for the region close to PbZrOj. There exists
morphotoropic phase boundary in PZT in the vicinity
of Zr/(Zr + Ti) = 0.52, and generally the crystal
structure of PZT on the Zr rich side of the phase
boundary is tetragonal, while the crystal structure
of PZT on the Ti rich side of the phase boundary is
rhombohedral. This invention has been made based on
the finding that an epitaxial crystal having a
composition in the vicinity of the morphotoropic
phase boundary and a {111} orientation shows
excellent dielectric characteristics. Curie
temperature Tc continuously changes between 230°C of
PbZrOa and 4 90°C of PbTiOs depending on the Zr/Ti
ratio .

- 29 -

10

Although the material gases for PZT have been
already described above, the method of this invention
will be further described taking a typical example,
in which Pb(C7Hi902)2, Zr (0-t-C,H9)4, Ti (O-i-CaH, ) , and O2
are used, with reference to FIG. 3. FIG. 3 is a
schematic view showing one example of MOCVD apparatus
for forming PZT films. In this apparatus, a cold
wall type of reactor 1 is provided with pre-heating
means 2 and a substrate 4 is placed on a heating
susceptor 3 in the reactor 1. Pb (CxiH, ,.0, ) ^ as a Pb
material 6 is in the solid state at room temperature,
therefore, it is heated in an oven 5 and vaporized
while blowing Ar as a carrier gas over its upper
portion. Zr(O t-C<,H9), as a 2r material 7 and Ti (O-i-
C3H7)4 as a Ti material are in the liquid state at
room temperature, therefore, they are heated and
vaporized while bubbling Ar as a carrier gas.
Reference numeral 9 denotes an argon cylinder numeral
10 an oxygen cylinder. The carrier gas may be N2 or
20 He. The air in the reactor 1 is evacuated through
filters 11 with a mechanical booster pump 12 and a
rotary pump 13 and discharged outside through a
hazardous material remover 14. The material gases
generated from the respective material sources are
mixed together and fed into the reactor 1 in the form
of a mixed gas. The mixed material gas reacts on the
heated substrate 4 to deposit PZT thereon.

15

25

- 30 -

The Pb/Zr/Ti molar ratio and the Oz/Pb molar
ratio of the material gas mixture are adjusted
depending on the desired PZT composition. For
example, Zr/{Zr + Ti) = 0.48 or 0.52 and Pb/(Pb + Zr
+ Ti) = 0.5. However, the Oj/Pb molar ratio need not
be very strictly adjusted, as long as a needed amount
or more of O2 and Pb is supplied.

As to the substrate for PZT, (111) Pt/Ti/SiOz/Si ,
Ir/TiOz/SiOz/Si and IrOj have been known as suitable
multi-crystal PZT growth substrates and (100)
SrRuO3/{100) SrTi03, (111) SrRuOs/dll) SrTiOs, (110)
SrRuOs/dlO) SrTi03 have been known as suitable
epitaxial crystal PZT growth substrates. However, in
this invention, a substrate is used which allows the
desirable growth of an epitaxial (111) PZT crystal.
Other substrates such as, for example, (111)
Pt//(100) YSZ//(100) Si and (111) Pt//(111)
YSZ//(111) Si can also be used (YSZ represents
yttrium-stabilized zirconia YZrOz) - Pt in the above
substrates can be replaced with Ir, SrRuOs, LaNiO, or
LaSrCoOa- YSZ can be' replaced with CeOa, MgO or SrO.
In this example, (111) SrRuOs/dll) SrTiOa is used as
the substrate 4. {111} oriented substrates other
than (111) oriented one can also be used as the
substrate 4 ,

As described above, the material gas mixture is
introduced into the reactor 1 so as to deposit PZT on

the substrate 4, and in this example, the material
gas is fed intermittently (in a pulsing manner) . Fo
example, the material gas feeding time is 5 to 10
seconds and the time interval is 0 to 20 seconds. A
valve 15 is used to start or stop the material gas
feeding, and at the same time, a valve 16 is used to
introduce a purge gas into the reactor 1 while the
material gas feeding is stopped. The introduction or
a purge gas ensures the intermittent deposition of
PZT.

The method of this invention has been described
with reference to the apparatus shown in FIG, 3;
however, the construction of MOCVD apparatus is not
limited to that shown in FIG. 3. For example, the
apparatus may have a vertical reactor.

The thickness of the ferroelectric material
thin film, such as PZT thin film, deposited on the
substrate is not limited to any specific one and
determined depending on its application. Generally,
it is 10 to 250 nm for the memory application, 1 to
10 pom for the actuator application, and about 10 |j.m
or less for the micro machine application. Since the
permittivity is saturated at a film thickness of
about 250 nm, the thickness of 250 nm or less is
common for the memory application.

When producing a ferroelectric memory, actuator
or micro machine using the lead zirconate titanate-

based material formed as above, the construction and
the production method can be the same as the
conventional ones .

As a substrate material that allows the
epitaxial growth of a lead zirconate ti tanat e-based
film, an oxide having a perovskite structure, such as
SrRu03, CaRu03, LaNiOa or LaSrCoOs, is useful. Pt, Ir,
IrOz also allows the epitaxial growth of a lead
titanate-based film if its substrate is properly
selected. Generally, the requirement that a
substrate has to meet to allow the epitaxial growth
of a lead zirconate titanate-based film is that the
difference in lattice constant between the substrate
and the intended zirconate titanate-based compound is
less than 10%.

There have been reported several cases in which
Pt, Ir or Ir02 is used to allow the growth of a one-
axialiy oriented film of a lead zirconate titanate-
based material, such as PZT, but no case in which Pt.
Ir or Ir02 is used to allow the epitaxial growth of
the same. However, as described above, if a
substrate of Pt, Ir or Ir02 is properly selected, PZT
can also be epitaxially grown on the substrate of Pt,
Ir or Ir02.

Further, if the substrate is electrically
conductive, it can be used as an underelect rode after
completing the film formation; therefore, such a

- 33 -

10

substrate is useful in constructing a high-
performance dielectric device. SrRuOa, CaRuOj, Lalvio
LaSrCoOs, and besides, Pt, Ir, IrOz are conductive
substrates.

Although the lead zirconate ti tana te-based
epitaxial film of this invention is useful as a
dielectric film such as ferroelectric film,
piezoelectric film or pyroelectric film, when it is
used as a constituent of a ferroelectric device,
piezoelectric device or pyroelectric device, it must
be formed an electrically conductive substrate. For
this purpose, as a conductive material that allou's
the growth of a lead zirconate t itanate-based
oriented or epitaxial film, an electrically
15 conductive material is useful which is selected from
the oxides having a perovskite structure such as
SrRu03, CaRuOa, LaNiOj and LaSrCoOj. If the substrate
is electrically conductive, it can be used as an
underelectrode after completing the film formation,
and therefore, it is useful in constructing a high
performance dielectric device. Metals such as Pt and
Ir also allow the formation of an epitaxial film, and
these are very useful in this invention from the
viewpoint of production economy.

These substrate materials may be used for only
the surface of a substrate. For example, SrRuOs can be
used as SrRuOa // SrTiOs.

20

25

"SA-

ID

15

20

25

The applications of the dielectric film of this
invention and the dielectric device including the
same are, not limited to, micro machines that use
electrostriction; piezoelectric devices for use in
MEMS and ink jet printer heads; ferroelectric devices,
such as FeRAM, that use high ferroelectic
- characteristics; devices, such as an optical shutter,
that use a large electro-optical effect expected from
a large permittivity change; and devices, such as IR
sensor and bolometer, that use pyroelectric
characteristics which are related to ferroelectric
characteristics .
[Examples ]
(Example 1)

Epitaxial deposition of PZT was carried out in
accordance with the method described in the examples
of Japanese Patent Application Laid-Open No. 2001-
220676, except that a vertical MOCVD apparatus was
used as shown in FIG. 4. The material feeding system
21 of this apparatus was the same as that shown in
FIG. 3, but as a carrier gas was used a nitrogen No
gas. A reactor 23 within an oven 22 was provided
with a substrate holder 24 equipped with a heater,
and a mixed material gas, which had been mixed in
advance, was fed onto the surface of each substrate
from above the substrates held in the substrate
holder 24 through a nozzle 25 shown in FIG. 5. The

- 35 -

nozzle 25 had a total length of 340 mm. The upper
portion 26, 150 inm long, of the nozzle was tapered
with its inside diameter reduced from 58 mm to 37 mm,
while the lower portion 27, 150 nnn long, was in the
5 form of a cylinder 1 . 5 mm thick and uniform in inside
diameter (37 mm) whose tip was flat. The nozzle was
used -to feed mixed material gas onto the surface of
each substrate, which was arranged at a relatively
close distance from the tip of the nozzle (the space

10 between the tip of the nozzle and the substrate

surface: 6 mm) in such a manner as to be parallel Lo
the same, and was designed to be able to feed a mixed
material gas uniformly onto the substrate surface
while avoiding the occurrence of turbulent flow of

15 the gas- Seven square substrates with sides 10 mm
were arranged on the substrate holder in such a
manner as to keep the space between the center of the
substrate holder rotation and the side of each
substrate facing the above center 13 mm and spacing

20 the seven substrates at equal intervals. And the
substrate holder was rotated when used,

PZT epitaxial films were formed on (100)
SrRuOs// (100) SrTiOs, (110) SrRuOa/ / { 1 1 0 ) SrTiOa and
(111) SrRu03//(lll) SrTiOs substrates at a deposition

25 temperature of 600°C by pulse MOCVD, in which

material gases were fed into the vertical reactor
intermittently, using Pb (C11H19O2 ) 2, Zr (O- t-C4H9 ) 4 ,

Ti (O-i-CsH?) « and O2 as starting materials. The
composition [Zr/(Zr + Ti) ratio, that is, y] of the
films was controlled while keeping the Pb/ ( Pb + Zr +
Ti) ratio constant, 0.50, and adjusting the amount of
material gases shared. The film thickness was
controlled while changing the deposition time.

- The heating temperatures for the above
materials of Pb, Zr and Ti were set at 142. 5°C, 36.0°c
and 42.0°C, respectively, and the carrier gas N2 was
flown at flow rates of 80, 60 and 60 cmVmin,
respectively. For Zr and Ti materials, bubbling of N2
gas was started 35 min before starting the film
formation to vaporize them. The material gases were
mixed prior to the introduction into the reactor and
the resultant mixed gas was fed onto the substrates
which were rotated at 1 . 0 rpm. The space between the
nozzle and each substrate was 6 mm at the time of the
mixed gas feeding. The total pressure of the reactor
was 8 torr and the partial pressure of oxygen was 6.5
torr. The film thickness was controlled while
changing the deposition time. The thickness of the
resultant films was 500 nm to 7000 nm (7 fjm) .

The crystal structure analysis of the produced
films was carried out with a high-resolution X-ray
dif fractometer provided with 4 axes (XRD, PANalytical
X'pert-MRD) and the composition analysis of the same
with a wavelength dispersion type of fluorescent X-

ray spectroscopy (XRF, PANalytical PW2404) . The
thickness of the films was measured with a contact
type film thickness meter, Dektak, an XRF and a
scanning electron microscope (FE-SEM, s-2500 Hitachi)

Upper Pt electrodes 100 join in diameter and 200
M.m in diameter were formed by electron beam
evaporation using a metal mask. The ferroelectric
characteristics and dielectric characteristics were
evaluated with ferroelectric testers RT6000, FCE-1
(TiDyo Corporation) , FCE-PZ (Toyo Corporation) and
HP4194A.

The electrostriction was measured with an
atomic force microscope (AFM, API3800 SIX, Nano-R,
Toyo Corporation) in combination with a ferroelectric
tester FCE-1 or FCE-PZ.

^~^^y diffraction analysis was conducted for
the PZT films formed on the (100) SrRuO,// { 100) SrTiCb
substrate, the (110) SrRuOa// ( 1 10 ) SrTiOa substrate
and the (111) SrRuOa// ( 1 1 1 ) SrTiOs substrate and
having composition ratios y = 0.75 ( rhombohedral
crystal), y = 0.48 (in the vicinity of morphotoropic
phase boundary) and y = 0.39 (tetragonal crystal).
FIG. 6 shows XRD patterns of PZT films formed on the
(111) SrRuOs// (111) SrTiOa substrate and having
composition ratios y = 0.75 (rhombohedral crystal), y
= 0.4 8 (in the vicinity of morphotoropic phase
boundary) and y = 0.39 (tetragonal crystal).

- 38 -

respectively .

The analysis confirmed that in any one of the
above three types of PZT films formed on the
substrate, there were observed no peaks other than
5 those identified as the PZT peaks. And the pole
figures confirmed that the films were epitaxially
grown. The half -width in the circumferential
direction in the pole figures was 8°. There have been
reported no PZT epitaxial films at least as {111}
10 orientated PZT films.

The half-width of the locking curve at 29 =
38.5^ in the {111} orientated PZT films was 0.6 to
0.7^ and the crystal orientation was almost perfect.

At the composition ratio y = 0.4 8 (in the
vicinity of morphotoropic phase boundary), there was
detected the coexistence of at least two of
tetragonal crystal, cubic crystal and rhombohedral
crystal. This case has never been reported before.
FIG. 7 shows one example of X-ray reciprocal mapping
images of (222) face and (114) face that shows the
existence of a mixed crystal and the completeness of
the crystals.

FIG. 8 shows the composition dependency of the
lattice constant of (100) PZT. The composition range
25 in the vicinity of the morphotoropic phase boundary
of this invention selected based on the lattice
constant was y <^ 0.40 to 0.65.

15

20

FIG. 9 shows the composition and crystal
orientation dependency of the relative permittivity
Sr- The figure confirms that relative permittivity s,
has a maximum in the range of Zr/(Zr + Ti ) = y = 0.4 0
to 0.65 in the vicinity of the morphotoropic phase
boundary independently of the crystal orientation and
is high in the (111) orientated film independently of
the composition.

FIG. 10 shows the composition and crystal
orientation dependency of the polarization-voltage
characteristics (P-E characteristics) of the PZT
films. The data are^ on the PZT films of y = 0.39
(tetragonal crystal), y = 0.48 (in the vicinity of
the morphotoropic phase boundary) and y = 0.75
(rhombohedral crystal) and (100) orientation, (110)
orientation and (111) orientation. The figure
confirms that the film having a composition in the
vicinity of the morphotoropic phase boundary and
(111) orientation shows particularly high
polarization Pr.

FIG. 11 shows the composition and crystal
orientation dependency of the relative permittivity-
voltage characteristics (C-E characteristics) of the
PZT films. The data are on the PZT films of y = 0.39
(tetragonal crystal), y = 0.48 (in the vicinity of
the morphotoropic phase boundary) and y = 0,75
(rhombohedral crystal) and (100) orientation, (110)

orientation and (111) orientation. The figure
confirms that the film having a composition in the
vicinity of the morphotoropic phase boundary and
(111) orientation shows particularly high relative
permittivity. As shown in FIG. 11, the film having a
composition of y = 0.48 shows Ae/AE of as high as 10
or more. The films having a composition within the
range of 0.43<y<0.57 preferably show As/AE of 3 or
more and their piezoelectric characteristics are also
good -

FIG. 12 shows the composition and crystal
orientation dependency of the piezorest icti vi ty-
voltage characteristics (S-E characteristics) of the
PZT films (2.5 ^m thick). The data are on the PZT
films of y - 0.39 (tetragonal crystal), y - 0.48 (in
the vicinity of the morphotoropic phase boundary) and
y = 0.75 (rhombohedral crystal) and (100) orientation,

(110) orientation and (111) orientation. The figure
confirms that the film having a composition in the
vicinity of the morphotoropic phase boundary and

(111) orientation shows particularly high
piezorestictivity .

FIG. 13 shows S-E curves of the films having a
composition of y 0.48 (in the vicinity of the
morphotoropic phase boundary) and orientations of
(100), (110) and (111) when applying unipolar
electric field thereto. The figure also confirms

that the film having a composition in the vicinity of
the morphotoropic phase boundary and (111)
orientation shows particularly high piezores t i ct i vi t \
Although FIGS. 9 to 13 show the data on y = 0.48, the
data obtained while changing the y value little by
little (including the data shown in FIGS. 6 and 7)
confirm that excellent results are obtained when y -
in the range of about 0.4 0 to about 0.65, about 0.4 3
to about 0.65, about 0.43 to about 0.57, and
particularly about 0.45 to about 0.55.

FIG. 14 summarizes and schematically
illustrates the composition and crystal orientation
dependency of the relative permittivity s^,
spontaneous polarization Ps, coercive electric field
Ec and residual dielectric polarization Pr of the PZT
epitaxial films
(Example 2)

PZT epitaxial films each having a (111)
orientation were formed in the same manner as in
example 1, except that the composition ratio was
Zr/ (Zr + Ti) = 0.53.

The characteristics of the resultant PZT films
were evaluated in the same manner as in example 1,
and the evaluation confirmed that the films had a
mixed crystal structure of tetragonal crystal and
rhombohedral crystal and had excellent dielectric
characteristics, like those in example 1. The half-

- 42 -

width of the tetragonal crystal was 0.9'" and that of:
the rhombohedral crystal was 0.7^. FIG. 15 shows one
example of X-ray reciprocal mapping images of the
(114) face of (111) orientated PZT films. The As/AE
5 of the films was 5.5.
(Example 3)

- PZLT epitaxial films each having a (111)
orientation were formed in the same manner as in

example 1, except that the composition ratio Zr/ (2r +
10 Ti) was changed.

The characteristics of the resultant PLZT films
were evaluated in the same manner as in example 1,
and the same results as in example 1 were obtained.
FIG. 16 shows the relationship between the value of

15 piezorestrictivity and Zr/(Zr + Ti) ratio of the
resultant PLZT films. The figure confirms that
piezorestictivity is improved when the Zr/(Zr 4- Ti)
ratio is within the range of 0.40 to 0.65. However,
when the Zr/ (Zr + Ti) ratio is less than 0.43, the

20 residual dielectric polarization Pr and the relative
permittivity tend to be inferior.
( Example 4 ) .

PZLT epitaxial films each having a (111)
orientation were formed in the same manner as in
25 example 1, except that as substrates were used
(111) Pt//{100)YSZ//(100)Si and

(lll)Pt//(lll)YSZ//(lll)Si. The (lll)Pt film could

- 43 -

be obtained by forming a Pt film at 680^C when
producing the substrates.

FIGS. 17 and 18 show the X-ray diffraction
charts of the PZT films formed on the
5 (111) Ft// (100) YSZ// (100) Si substrate and the

(111) Ft// (111) YSZ// (lll)Si substrate. The figures
confirm that PZT epitaxial films each having a (111)
orientation are obtained. In the (111) orientated
PZT film formed on the ( 1 1 1) Pt // ( 1 00 ) YSZ// (1 00) Si
10 substrate shown in FIG. 18, the half width of the
locking curve at 9 = .19.3° was 4.9°.
(Example 5)

PLZT films each having a composition
represented by the formula Pbo.94Lao.06Zro.48Tio.52O3 and a

15 (111) orientation were formed in the same manner as
in example 1, except that part of the Pb material, 6
mol%, was replaced with lanthanum material La(EDMDD)5.

The characteristics of the resultant PLZT film.s
were evaluated in the same manner as in example 1 and

20 the similar results as above were obtained. The

piezoelectric characteristics were improved compared
with the PZT films having the corresponding
composition PbZro.48Tio.52O3.

Although it has been known that if part of Pb

25 of PZT is replaced with a small amount of La, the

resultant PLZT has improved characteristics compared
with the PZT, the results confirmed the fact.

(Example 6)

A PZT film 2 jam thick was formed on a

(llDSrRuOa// (111) SrTi03 substrate in the same manner
as in example 1;. except that y = 0.59. The
evaluation of C-E characteristics of the film showed
that the As/AE was 3.2 and the piezoelectric
characteristics were good. XRD measurement revealed
that the film was a (111) orientated mixed crystal
system .

The Pb composition ratio may be stoichiometric
ratio, but. it may also be excessive compared with Zr
and Ti within the range of 15%.